So it went on Wednesday evening, when Mr. Trump appeared to revert to partisanship as usual, just in a softer tone of voice. Here in Wisconsin, he embarked on his 38th campaign rally since assuming the presidency with a bit of rhetorical jujitsu, managing to weave jabs at the news media and Democrats into an opening call for Americans to “come together in peace and harmony.”

“We should not mob people in public spaces or destroy public property,” Mr. Trump said in a thinly veiled reference to his latest turn of phrase — “jobs not mobs” — and a castigation of how liberals reacted to Justice Brett M. Kavanaugh’s battle to be confirmed to the Supreme Court amid multiple accusations of sexual misconduct.

The president flicked at a suggestion popularized by liberals and some members of the news media who have suggested his nationalist views are akin to Adolf Hitler’s: “No one should carelessly compare political opponents to historical villains.”

And somehow, Mr. Trump made the day’s news about his own problems with the news media. He called on journalists “to set a civil tone” and to “stop the endless hostility and constant negative and often false attacks and stories.”

Then Mr. Trump again directed the crowd’s attention to his bipartisan efforts: “By the way, do you see how nice I’m behaving tonight?” he asked. “Have you ever seen this? We’re all behaving very well!”

(Minutes later, the president broached the topic yet again: “I think we will be bipartisan on infrastructure.”)

Still, the performance by Mr. Trump and the slate of Wisconsin Republicans who took the stage here served as further confirmation that, with less than two weeks to go until a round of midterm elections in which the leadership of the House is at stake, not even reports of explosive devices could do much to halt months of highly divisive messaging at campaign rallies.

Mr. Trump did address the reports in his opening remarks, calling the episodes “an attack on our democracy itself” and promising swift justice.

“Such conduct must be fiercely opposed and firmly prosecuted,” the president said. “We want all sides to come together in peace and harmony. We can do it.”

Two other Republicans who took the stage here at an airport hangar in the 4,000-person town of Mosinee began their speeches with a short disclaimer — essentially, terrorism is bad — before denouncing Democrats for their immigration policies and the cost of health care.

Speaker Paul D. Ryan had some trouble breaking through a “Build the Wall!” chant.

“Let me just say something that I think needs to be said on a day like today,” Mr. Ryan said.

“Build the wall!” a group in the crowd shouted.

Mr. Ryan replied that he would “get to that,” cracking a smile.

“Build the wall!” the group yelled, louder that time.

“Did you see the news this morning about these devices?” Mr. Ryan eventually asked. “That is terrorism. There is no place for that in our democracy. We reject that, and I just want to say thank God for our law enforcement.”

Gov. Scott Walker, a Republican who is battling for a third term, also briefly touched on those reports.

“An attempt to engage in a terrorist act against any American is an attack on every American,” he said.

In his remarks earlier at the White House, Mr. Trump said the packages of explosives were sent to “current and former high-ranking government officials,” without specifying the intended recipients: former President Barack Obama; the former Democratic presidential nominee Hillary Clinton; John O. Brennan, the former C.I.A. director; and Representative Maxine Waters, Democrat of California — four of the president’s favorite political targets. Another device apparently intended for the man who served as Mr. Obama’s attorney general, Eric H. Holder Jr., was misaddressed.

The package for Mr. Brennan, which included an unidentified white powder, was sent to the New York offices of CNN, the cable news network that Mr. Trump regularly denigrates. New York’s mayor, Bill de Blasio, called the suspicious packages “an effort to terrorize.”

Mr. Brennan has been an outspoken critic of Mr. Trump’s, ultimately leading the president to strip him of his security clearance. Mr. Brennan works as a paid consultant to MSNBC, not CNN. The return address on the package sent to CNN was that of Representative Debbie Wasserman Schultz, Democrat of Florida and a former Democratic National Committee chairwoman.

“We will not be intimidated by this attempted act of violence,” Ms. Wasserman Schultz said in a statement on Wednesday evening.

Several of the president’s past rally targets seemed skeptical that he would temper his language, and others suggested that Mr. Trump’s words had put his political opponents in danger. Nancy Pelosi of California, the House Democratic leader, and Chuck Schumer of New York, the leader of the Senate Democrats, called on the president to take back comments he has made that condone acts of violence — last week, Mr. Trump praised a Republican congressman for body-slamming a reporter.

They said in a joint statement that “President Trump’s words ring hollow until he reverses his statements that condone acts of violence.”

At a conference on Wednesday in Texas, Mr. Brennan seemed cautiously optimistic.

“What he said today is what a president should be doing,” Mr. Brennan said. “But follow up on those words with actions, and with his future comments. I’m hoping maybe this is a turning point.”

The president has shown little regard for refraining from delivering divisive messages hours after more sober missives delivered in Washington, but he did not call out his frequent rally targets, several of whom received packages on Wednesday, by name. And though “lock her up” chants rang out, Mr. Trump did not bring up Mrs. Clinton.

The president instead directed the crowd to his usual potpourri of factually dubious claims about Democratic policies, lingering on the fear-first immigration messaging his White House hopes to harness in time for the elections.

“Democrats oppose any effort to secure our border,” Mr. Trump said, once again glossing over the fact that Democrats favor border security measures — but not the construction of the president’s long-promised wall on the southwestern border. Mr. Trump then hinted that he would be following through on repeated suggestions that he would send the military to the border, even though the military is prohibited from engaging in policing activities.

“Wait till you see what happens over the next few weeks. You’re going to see a very secure border. You just watch,” he said. “And the military is ready. They’re all set. They’re all set. They’re all ready and there is nobody like them.”

Through it all, Mr. Trump urged his supporters to pay attention to how quietly he was speaking. He tried, at different points, to emphasize the positive.

“Kanye West likes me,” the president said. “Interesting guy.”

“Kanye’s an idiot!” a lone rallygoer shrieked in reply.

Indeed, at times, it was clear some attendees did not want to participate in a lower-decibel rally.

“I’m trying to be nice,” the president said in a reminder that seemed as much meant for himself as it was for the crowd.